1. Field of the Invention
The present invention relates to an upper mount in a suspension system of an automotive vehicle, and more particularly to a fluid-tight sealing arrangement in the upper mount.
2. Discussion of Related Art
JP-A-58-77945 discloses an example of a suspension upper mount of the type described above, in the form of a strut mount as shown in FIGS. 5A and 5B.
The upper mount shown in FIGS. 5A and 5B is used in a strut type suspension system arranged to connect a wheel (tire) 200 of an automotive vehicle to the body of the vehicle in a vibration-damping fashion. The wheel 200 is rotatable about an axis of an axle 202 attached to a spindle. The vehicle body includes a panel 206 to which the spindle 204 is connected through a lower arm 208 and suspension bushings 210.
The strut type suspension system includes a shock absorber 212 and a coil spring 214, as major components thereof. The shock absorber 212 has a cylinder 216, and a piston rod 218 which extends upwards from a piston slidably fitted within the cylinder 216, such that an upper end portion of the piston rod 218 is located outside the housing of the cylinder 216. The shock absorber 212 is connected at its lower end portion to the spindle 204.
The strut type suspension system further includes as a major component an upper mount 220 in the form of a strut mount disposed between an assembly of the shock absorber 212 and the coil spring 214 and the vehicle body panel 206, for elastically connecting the above-indicated assembly 212, 214 to the panel 206. The upper mount 220 includes as a major component an elastic body 227, as shown in FIG. 5B.
The upper mount 220 is provided with an upper spring seat 222, while the housing of the cylinder 216 of the shock absorber 212 is provided with a lower spring seat 224. The coil spring 214 is disposed around the shock absorber 212 such that the upper and lower ends of the coil spring 214 are held in abutting contact with the respective upper and lower spring seats 222, 224.
In the strut type suspension system constructed as described above, the shock absorber 212 and the coil spring 214 cooperate to damp or absorb a vibrational load transmitted from the wheel 200 running on a roadway surface. On the other hand, the upper mount 220 including the elastic body 227 as its major component functions to damp or absorb a portion of the vibrational load that cannot be absorbed by the shock absorber 212 and coil spring 214, so that the transmission of the vibrational load to the vehicle body (panel 206) is inhibited by the upper mount 220.
The upper mount 220 includes a metal housing 226, and a main body 229 which is accommodated in the metal housing 226 and which has the elastic body 227 as its major component.
The housing 226 consists of an upper member 228 and a lower member 230 welded together, and includes a cylindrical wall portion 232, an upper wall portion 234, a bottom wall portion 236, and a fixing flange portion 240 which extends radially outwardly from an axially intermediate part of the cylindrical wall portion 232. The upper and lower members 228, 230 of the housing 226 are welded together at the fixing flange portion 240, and the upper mount 220 is fixed with screws 242 to the vehicle body panel 206 at the fixing flange portion 240 of the housing 226. The upper and lower wall portions 234, 236 have respective central openings 244, 246.
The elastic body 227 is a generally cylindrical or annular block formed of a rubber composition, and is provided with an inner rigid member in the form of an inner metal member 248 disposed in a radially central portion thereof. The piston rod 218 is fixed with a nut 250 at its upper end portion to the inner metal member 248 of the elastic body 227.
The elastic body 227 has an upper circumferential groove 252 and a lower circumferential groove 254 which are open in its respective upper and lower surfaces and which are formed with suitable depths, in the circumferential direction of the cylindrical wall portion 232. The elastic body 227 further has three stopper portions 256 formed on its upper surface, so as to protrude upwards, such that the three stopper portions 256 are spaced apart from each other in the circumferential direction of the housing 226. The stopper portions 256 are held in pressing contact with the lower surface of the upper wall portion 234 of the housing 226.
The three stopper portions 256 spaced apart from each other by a suitable spacing distance in the circumferential direction of the housing 226 cooperate with the upper surface of the elastic body 227 and the lower surface of the upper wall portion 234 of the housing 226, to define spacings S through which the upper central opening 244 of the upper wall portion 234 is held in communication with the upper circumferential groove 252.
In the upper mount 220 constructed as described above, a vertical oscillating movement of the piston rod 218 is absorbed by elastic deformation of the elastic body 227, so as to prevent the transmission of the vibrational load from the wheel 200 to the vehicle body. The upper and lower circumferential grooves 252, 254 are formed in the elastic body 227, for the purpose of giving the elastic body 227 a relatively soft spring characteristic in the vertical direction, to thereby improve the vibration damping or absorbing function of the elastic body 227. On the other hand, the stopper portions 256 are provided to prevent an excessive amount of elastic deformation of the elastic body 227 in the vertical direction upon application of a large vibrational load to the elastic body 227.
It is noted that the spring stiffness of the elastic body 227 tends to gradually decrease from the initial or nominal value with an increase in the cumulative operating time of the upper mount 220 with repeated elastic deformation of the elastic body 227 in the vertical direction. Accordingly, the amount of vertical elastic deformation of the elastic body 227 per unit amount of the input vibrational load gradually increases during the service life of the upper mount 220.
In the upper mount 220 of the type discussed above, the elastic body 227 is simply accommodated within the metal housing 226, without the elastic body 227 being bonded at its outer circumferential surface to the inner circumferential surface of the cylindrical wall portion 232 of the housing 226. In this arrangement, a considerably large amount of elastic deformation of the elastic body 227 in the vertical direction may undesirably cause a sliding displacement of the elastic body 227 at its outer circumferential surface relative to the inner circumferential surface of the cylindrical wall portion 232, resulting in undesirable generation of a noise due to the sliding displacement.
Further, the sliding displacement of the elastic body 227 leads to a problem of an increased amount of wear of the outer circumferential surface of the elastic body 227.
To solve the problems of the upper mount 220 of FIG. 5B, the upper mount 220 is modified as shown in FIG. 6, such that the elastic body 227 is formed by vulcanization within an outer metal sleeve 258 such that the formed elastic body 227 is bonded at its outer circumferential surface to the inner circumferential surface of the outer metal sleeve 258. The thus prepared main body 229 consisting of the elastic body 227 and the outer metal sleeve 258 is fixed within the metal housing 226 such that the outer metal sleeve 258 is press-fitted in the cylindrical wall portion 232, with the outer circumferential surface of the metal sleeve 258 held in pressing contact with the inner circumferential surface of the cylindrical wall portion 232.
In the upper mount 220 described above, the upper central opening 244 formed through the upper wall portion 234 may or may not be closed by a cap. In the absence of the cap, an aqueous component such as water which has entered through the upper central opening 244 flows into the upper circumferential groove 252 through the spacings S, resulting in a problem that the aqueous component is accumulated in the circumferential groove 252.
The aqueous component accumulated in the upper circumferential groove 252 may cause corrosion and rusting of the metallic material of the outer metal sleeve 258, and a risk of separation or removal of the elastic body 227 from the outer metal sleeve 258.